1. Field of the Invention
This invention relates generally to systems for transmitting data along optical paths, and more particularly, to a multiple access network wherein a single, continuous-wave optical carrier which propagates through fiber optic cable is successively modulated at plural data access nodes by respective optical modulator stages in response to respectively associated local data streams.
2. Description of the Related Art
Known multiplexing multiple-access communication networks are complicated and expensive to build and operate. One typical system is shown in FIG. 1, and is of the multiplexing regenerator type wherein the optical carrier is regenerated at each node. As shown in FIG. 1, this known system employs multiplexer/regenerator nodes 10 through 13, at each of which digital data from multiple sensors (not shown) is supplied to a multiplexer which conducts the multiplexed digital data to a regenerator. Each regenerator receives, in this known arrangement, an optical signal which is converted to an electrical signal. The electrical signal is then multiplexed with the electrical multiplexed data from the multiplexer. The electrical signal having the combined information is convened to an optical signal and transmitted by an optical fiber to the next successive regenerator.
There is clearly a need for a system which eliminates the optical/electrical and electrical/optical conversions as prerequisites to the multiplexing of node data. Each such conversion, in addition to requiring the use of expensive and complex hardware, also requires significant consumption of electrical energy, thereby requiring a high capacity electrical conductor to be provided in conjunction with the optical fiber for remote sensing. The high supply voltages complicates the cable design.
It is, therefore, an object of this invention to provide a multiple-access communications network which propagates a single, continuous-wave optical carrier which is successively modulated without the need for electrical/optical conversion at each access node of the network.
It is another object of this invention to provide a multiple-access communications system wherein the expense of optical carrier regeneration is avoided.
It is also an object of this invention to provide a multiple-access communications system which affords a significant improvement in overall data throughput over that afforded by time-division multiplexing (TDM) arrangements.
It is a further object of this invention to provide a multiple-access communications system which reduces expense, power consumption, and complexity by eliminating the need for a full complement of regenerator functions at each location, as required in known systems which multiplex local data.
It is additionally an object of this invention to provide a multiple-access communications system which achieves high reliability and survivability, and which is tolerant of node failure.
It is also another object of this invention to provide a multiple-access communications system which can be driven by a single laser source.
It is yet an additional object of this invention to provide a multiple-access communications system which has the capacity to support hundreds of nodes.
It is still another object of this invention to provide a multiple-access communications system wherein power consumption is reduced by performing all modulation in the optical domain.
It is also a further object of this invention to provide a multiple-access communications system.